**7.1 Gas guidance**

If the fermenters are filled regularly with biomass which is air-tight heated and regularly stirred, the biogas will be formed within a matter of days where the formation of biogas is a complex and delicate process. The organic fats which cover high rates contained in the substrates are digested by various kinds of bacteria, this is a starting point for the development of the gas, the contents are continuously stirred, the gas drives slowly to the top of the container and it consists of approximately 50 to 70% methane, carbon dioxide, water vapor, hydrogen, and hydrogen sulfide. As water vapor and hydrogen sulfide are problematic for the utilization of the gas maker, it is necessary to purify the biogas.

The gas is first cleaned from water vapor. The condensed water is collected and a condensation shaft pumps it out. On the other hand, the aggressive trace gas hydrogen sulfide is now extracted from the biogas in a biological desulfurization unit, by introducing air to the container certain bacteria culture which is able to establish colonies on chains. The bacteria decompose the hydrogen sulfide to harmless sulfa and water. The almost unpressurized biogas is then fed into a compressor where it is watered up to 70 mbar pressure later required for burning. In order to completely condense any reaming water vapor freeing biogas of any suspending matters, the biogas is subjected to a washing brine process, this is carried out at almost a freezing point, so that the gas is cooled down to a temperature of 5 degrees. In order to control the purification of the gas, the biogas is constantly tested with an online measuring system which records the amount of methane, hydrogen sulfide, and carbon dioxide. This guarantees a high degree of efficiency and security. In case of any over production of biogas, it is necessary to operate a gas flame for the unburned methane gas that escapes to the atmosphere which is harmful for the environment.

Using 15,000 tons of biomass per year, the plant produces a total of 500 kW of electricity and heat. The optimal gas processing engines can run several years with the minimum of maintenance costs. Up to 30% of the waste heats from the water cooling the engine is used in the heat exchanger and the fermenter so that no additional heat is required, the remaining heat can also be used profitably to heat industrial plants and houses. The electric power generated by the Combined Heat and Power Plant (CHP) is converted to high voltage and then the electricity can be fed into the grid who meets the annual requirement of around 1000 households.
